Funds are requested to study the neural mechanisms underlying three- dimensional (3D) shape and size perception in somatosensory system. While the perception of local surface features is based on the activity in the mechanoreceptive afferents innervating the skin, gross object features such as shape and size are based on hand and finger position and cutaneous information from multiple points of contact with the object. Project 1 concentrates on how information is integrated from the multiple points of contact; This project (3) concentrates on the role of hand and finger position in 3D form processing. The aim is to study how information from tactile and proprioceptors within and between digits are integrated in SI and SII cortex of the awake monkey to provide information about the 3D shape and size of objects. Aim 1 is to investigate the processing of shape information by studying the integration of tactile information across adjacent digits positioned at different combinations of flexion, simulating contact with objects with varying shapes. Aim 2 is to investigate the processing of information about object size by studying how digit spread affects the responses of somatosensory neurons to local patents of stimulation. Two modes of stimulation, active and passive, will be used. In the passive mode stimuli that are or are not consistent with a single curved surface (aim 1) or stimulate an object of a specified size (aim 2) will be applied to the hand while the animal performs a tactile match-to-sample task. In the active mode, the animal actively moves it fingers to contact the stimuli that vary in curvature and size. In this manner we will study neuronal response tuning for object size and shape in various areas in the somatosensory cortex and determine and whether the tuning differs during active and passive touch.